The draw and iron (D&I) process for forming one-piece metallic can bodies, notably can bodies formed from aluminum alloys and steel, has become the dominant method for producing beverage containers for such products as beer and soft drinks.
In this process, circular blanks are punched from sheet metal and drawn into shallow cups in a first apparatus, commonly known as a cup maker.
These cups are then fed to a second apparatus, called a body maker or D&I press, where the cups are reformed by redrawing and ironing into their final container shape.
Subsequently, the container bodies are trimmed, necked and flanged to their final size.
In a continuing effort to reduce metal usage, weight and cost of the containers, container bodies have been designed to enable the containers to be formed from thinner sheet metal. For example, at one time aluminum alloy cans were formed from sheet metal having a thickness of about 0.015". More recently, however, these containers are being formed from metal as thin as 0.0129".
The decreased metal thickness, coupled with the increasing complexity of the bottom structure required for sufficient strength in the can, has led to a problem in can formation. The shallow cups entering the body maker are mechanically held against the leading edge of a redraw die by a cup holder positioned within the cup. A punch member passes through the cup holder, carrying the cup through the redraw die and a series of ironing dies, with the punch bottoming on a bottom former which, with the punch, forms the bottom surface structure of the container. The decreased metal thickness, coupled with the increased bottom structure complexity of modern cans, has produced wrinkles in the bottom structure of the container, due to slippage of the metal during the redraw operation.
The known mechanical cup holders are limited in the pressure they can apply to the cup against the redraw die. This limitation results from the length of axial movement required for the cup holder unit, as well as the stresses placed on the cup holder unit by its mechanical linkages.
It is thus a primary objective of the present invention to provide an improved cup holder mechanism for a can making body press which is capable of increasing the holding pressure of the cup holder during redrawing of the cup, thereby reducing substantially or eliminating wrinkles in the metallic containers formed therefrom.